In multi-hop wireless networks, a node can be equipped with multiple radios, each radio with multiple-input and multiple-output (MIMO) antenna technology. MIMO is the use of multiple antennas and advanced signal processing techniques at the physical layer of both the transmitter and receiver to improve communication performance. It offers significant increases in data throughput via spatial multiplexing or spatial reuse, without consuming additional bandwidth. In spatial multiplexing, MIMO can allow transmitting multiple independent data streams simultaneously over the MIMO antenna elements, each stream is transmitted from a different transmit antenna element in the same frequency channel. If these signals arrive at the receiver antenna array with different spatial signatures, the receiver can separate these streams. MIMO link can also suppress interference from neighboring links. Multiple streams can be transmitted simultaneously with interference suppressed in the same vicinity using the same frequency channel as long as the total number of streams (data streams and interference streams) is not greater than the number of receiving antennas. Furthermore each node equips multiple radios and can simultaneously operate on multiple channels. Of course, the total number of available channels is limited. The performance of a multi-hop wireless network depends on the channels that radio nodes operate and the MIMO streams that a radio transmits. The operating channel of a radio and the number of streams that a radio can transmit are inter-dependent.
In one prior art scheme, channel assignment has been studied in multi-radio multi-hop wireless mesh networks. However, the previous work has not considered the effect of MIMO or spatial multiplexing or spatial reuse on channel assignment. In another prior art scheme, the capacity gain of stream control in single-channel MIMO wireless mesh networks has been investigated. However, a single channel was used and the channel assignment was not considered. Channel assignment and MIMO stream control are inter-dependent and also depend on the traffic demand, data routing and transmission scheduling in multi-radio, multi-channel, multi-hop, MIMO wireless networks (M4 wireless networks). They should be determined jointly with data routing and transmission scheduling to obtain the optimal performance.
To obtain full benefits of multi-radios and MIMO technique, the channel assignment and the number and mode of MIMO stream transmissions for a radio should be determined jointly. In addition, data routing and transmission scheduling should also be considered while determining how to assign the operating channel of the radios (called channel assignment) and select MIMO streams and modes to transmit/receive for radios (called stream control) in multi-radio, multi-channel, multi-hop wireless networks with MIMO links. In the past, channel assignment and stream control has not been jointly determined nor has data routing and transmission scheduling been taken into consideration when performing channel assignment and stream control, in particular for multi-radio, multi-channel, multi-hop wireless networks with MIMO links.